To approach Atlantis itself a Worldstone was required as well, with darkest night soon to rule the western sea.

And you finally align the worldstone with the moonstone.
So for example the West Sea does not have to be aligned with the horns. It needs to be aligned with the New Moon, after the moonstone itself has been aligned with the sunstone (and the sunstone has been aligned with the horns).

You have to align the sunstone like you did on the first door.
And then align the moonstone to the sunstone (not the horns)

Thank you! I was stuck and this worked! Think of it as continuing where you left off, put the correct sun in the first riddle (from the dig site) to the horns and then, leaving that sun aligned with the horns, match the sun and moon combo from the second riddle.